Sensory and supporting cells derive from progenitor cells lining the developing cochlear duct. Evidence suggests that sensory cell regenerate in the vestibular sensory organs in many species, including mammals, and in the auditory organ in chicks. Recent reports suggest that sensory cells may regenerate following the degeneration of the hair cell induced by aminoglycoside in the mammalian organ of Corti in culture with retinoic acid. Other investigators demonstrated that retinoic acid may be responsible for inducing supernumerary sensory cells of organ of Corti culture's from embryonic mice. They speculated that this process requires cell "conversion" from supporting cells without cell division. These organ culture models provide an opportunity to address research questions regarding the fundamental mechanism(s) involved in the differentiation of sensory hair cells. The long term goal of the project is to increase understanding of the cellular and molecular mechanism(s) involved in the development of sensory hair cells during organogenesis and sensory regeneration. The identification of the "precursor" cell which gives rise to the hair cell is the ultimate project goal. Once the "precursors" are identified, attempts will be made to isolate and immortalize them. An immortalized cell line capable of differentiating into hair cells is immensely useful to test the function of hair cell specific genes. The short term objectives are: 1) establish organ culture techniques for organ of Corti; 2) determine if cell division is involved in regeneration; and 3) document the cellular process of sensory differentiation/regeneration using light and electron microscopy. Modified methods to maintain the organ of Corti in culture up to two weeks after explanation have been developed. The experiments to reproduce the results of Lefebvre and Warchol are underway.